Improvement in countersinks



UNITED STATES PATENT @Errea w VILLIAM B. ERSKINE, OF NEW YORK, N. Y.

IMPROVEMENT IN COUNTERSINKS.

Specification forming part of Letters Patent No. 179,778, dated July 11,1876; application tiled April 28, 1876.

To all whom it may concern:

. Be it known that I, WILLIAM B. ERsKINE, of New York city, in the Stateot' New York, have invented certain Improvements in Gountersinks, ot'which the following is a specification: A

I employ two countersinkingcutters. The outer lace ot' each cutter is aportion of a cone, so as to afford a bearing on considerable surface. Itis thus less liable to be disturbed in position by knots or other hardplaces. Furthermore, to avoid side pressure and strain upon the bit,consequent upon the cutting device being upon one side only, as inprevious devices of this character, I deem it important that the sameshould be upon opposite sides, and, acting with equal force in oppositedirec. tions, the bit is tirmly held in the center.

The accompanying drawings form a part of this specification, andrepresent what I consider the best means of carrying out the invention.

Figure l is a side elevation. Fig. 2 is a corresponding elevation turnedquarter around. Fig. 3 is a horizontal section on the line S S; and Fig.4 is a horizontal. section on the line T T, seen from below.

Similarletters ot'referenccindicatelike parts in all the figures.

A is an ordinary bit, adapted to bc turned by a suitable bit-stockorother device. (Not shown.) B1 B2 are tw( nearly corresponding cutters,formed with a groove adapted to rcceive the side of the bit. C isasti-ap firmly secured to the part B1 by means of a rivet, c. The partBZis milledout to t within l[he strap, and to move toward oraway fromits mate B1, as required in adapting it to larger or smaller bits. D isapinching-screw, which, on being turned, applies the parts B B2 forciblytogether, clamping the device firmly upon the bit at the de- `siredelevation. It' the bit is small, the screw A'D requires to be turned soas to drive the parts B1 B2 nearly together. If the bit is large, thescrew is driven in but a little way before al1 the parts come to a firmbearing.

The bodies of the cutters B1 B2 are cylindrical. The strap C is, bypreference, let into both and smoothly finished; but this is notabsolutely essential. The strap may, it' preferred, for strength orother reasons, be allowed to extend quite around the part B1, beingpartially or entirely let into the body of the latter or not, as may bepreferred. The necessity for maintaining a clear space to allow thescrew D to sweep around prevents.

any special advantage from being realized from reducing the dimensionson the opposite side.. A

The shank ofthe bit along that part where the countersink is usuallyrequired to be set is somewhat smaller than the hole which it has bored,and it is importantto perfect work that the countersinking device becentering. A single cutter is liable, on the one hand, to draw with itsciittiligedge, or, on the other hand, to be pressed away by theresistance of the material against the same.

My invention overcomes the difculties incident to the use'of a singlecutter under such WM B. ERSKINE.

Witnesses:

JESSE FE'r'rIs, WM. MILNE, Jr.

